Seal rings for potable water applications

ABSTRACT

A cemented carbide seal ring has at least one hard phase in a binder phase based on Co, Ni and Fe which results in a content Fe, Ni and Cr of less than 50 μg/l of each in a leach test with deionized water at 85° C. performed according to the requirements of British Standard BS6920: Section 2.6: 1996.

FIELD OF THE INVENTION

[0001] The present invention relates to cemented carbide seal rings forpotable water applications satisfying new demands of Fe, Ni and Crcontents.

BACKGROUND OF THE INVENTION

[0002] In the description of the background of the present inventionthat follows reference is made to certain structures and methods,however, such references should not necessarily be construed as anadmission that these structures and methods qualify as prior art underthe applicable statutory provisions. Applicants reserve the right todemonstrate that any of the referenced subject matter does notconstitute prior art with regard to the present invention.

[0003] Cemented carbide for corrosion resistance demanding applicationssuch as seal rings, bearings, bushings, hot rolls, etc. generally has abinder phase of Co, Ni, Cr and Mo, where the Cr and/or Mo addition actas corrosion inhibitors. An example of such a cemented carbide isdisclosed in U.S. Pat. No. 4,497,660.

[0004] U.S. Pat. No. 6,010,283 and related patents disclose a cementedcarbide with Co—Ni—Fe binder phase with 40-90 wt. % Co and 4-36 wt. % ofeach of Fe and Ni.

[0005] In cemented carbide seal rings for potable water applications Coand Ni-based binder phase cannot be used because of insufficientcorrosion resistance. Instead cemented carbide with binder phase basedon Ni and Cr have to be used. In the newly approved British standardBS6920, a cemented carbide to be used in potable water applications musthave a content of Fe, Ni and Cr of less than 50 μg/l of each, asmeasured in a leach test with deionized water at 85° C. must befulfilled, which is not possible with presently used cemented carbideseal rings.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the present invention to provideseal rings for potable water applications fulfilling the demands ofBS6920.

[0007] It has now surprisingly been found that a cemented carbide with abinder phase combining Fe, Ni, Co, Cr and Mo gives significantimprovement in corrosion resistance. This cemented carbide materialpossesses a corrosion resistance on the order of stainless steel whenplaced in hot water. Thus, the cemented carbide of the present inventionis able to satisfy the demands of BS6920. As a result the corrosionresistant cemented carbide can be used in seal rings in potable waterapplications according to BS6920. Thus a seal ring with the corrosionproperties of stainless steel but with the wear resistance of cementedcarbide is obtained.

[0008] According to the present invention there is now provided cementedcarbide seal rings consisting of at least one hard phase in a binderphase based on Co, Ni and Fe fulfilling the requirements of BS6920.

[0009] According to one aspect, the present invention provides acorrosion resistant carbide seal ring comprising a hard phase and abinder phase, the ring having a high resistance to leaching such thatless than 50 μg/l of each of Fe, Ni and Cr leaches into deionised waterat 85° C. when subjected to the procedure set forth in British StandardBS6920, Section 2.6, 1996.

BRIEF DESCRIPTION OF THE DRAWING

[0010]FIG. 1 shows the microstructure in 1500× magnification of acemented carbide according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Cemented carbide seal rings according to the invention shouldhave a content of binder phase from 5 to 15 wt. %, preferably 8 to 11wt. %, most preferably about 9 wt. %, with the remainder WC with anaverage grain size of 1.0 μm to 5 μm. The binder phase should be basedon Fe, Co and Ni with a composition 35-45 wt. % Fe, 15-50 wt. % Co andthe remainder Ni. The Fe/Ni ratio should be 1-1.3. Further, the binderphase should preferably contain Cr and possibly Mo, in addition todissolved W. The following relation for the total Cr content shall besatisfied.

[0012] 0.05<wt. % Cr/(100-wt. %WC)<0.15, preferably 0.055<wt. %Cr/(100-wt. % WC)<0.11, most preferably about 0.065<wt. % Cr/(100-wt. %WC)<0.085.

[0013] The amount of Mo shall be 0.1-3 wt. %, preferably <0.5 wt. %.

[0014] The total carbon content shall be in the interval of6.13-(0.05±0.007)×binder phase (Co+Ni+Fe) content (wt. %).

[0015] A certain graphite porosity on the order of <CO2 can be acceptedin the interior of the ring, but in the surface region, where corrosioncould occur, the graphite can act as a galvanic element and thereforeshould be avoided. A surface zone thicker than 200 μm free of graphiteshall therefore be present.

[0016] The cemented carbide according to the present invention is madeby conventional powder metallurgical methods. Powders forming the hardconstituents and prealloyed Ni, Fe and Co powders forming the binderphase are wet milled together, dried, pressed to bodies of desired shapeand sintered. The powder mixture shall have such a carbon content togive a carbon content of the sintered bodies according to abovespecified carbon content interval. For the binder phase contentsaccording to the invention a temperature in excess of 1550° C. issuitable. Cooling from sintering temperature shall be made as quickly aspossible generally at a speed in excess of 15° C./min down to 1100° C.

EXAMPLE 1

[0017] Cemented carbide for seal rings according to prior art were madewith the composition of 91 wt. % WC, 8 wt. % Ni, 0.7 wt. % Cr, 0.3 wt. %Mo. Two types of rings with dimension: OD=40 mm, ID=30 mm, height=5 mm(2200 mm²) and with dimension: OD=39 mm, ID=31 mm, height=3 mm (1540mm²) respectively, were manufactured for testing.

[0018] The rings were sintered at 1520° C. and had a carbon content of5.64 wt. % after sintering and an average WC grain size of 1.5 μm.

[0019] Seal rings according to the invention were made for testing withthe same dimensions as above.

[0020] The composition of the cemented carbide according to theinvention was: WC: 91.0 wt. %  Fe-Ni-Co alloy: 8.0 wt. % Mo: 0.3 wt. %Cr: 0.7 wt. %

[0021] The composition of the used FeNiCo-binder alloy was: Fe: 40.5 wt.% Ni: Remainder Co 21.1 wt. % Total C 0.014 wt. %  Total O 0.61 wt. %

[0022] The grain size of the WC phase was 1.5 μm.

[0023] The rings were sintered at 1520° C. in vacuum for 1 hour.

[0024] The physical properties after sintering were as follow: Density14.54 g/cm³ Hardness 1200 HV3 Porosity A00B00C00

[0025] The carbon balance was close to eta-phase formation.

[0026] A good milling and wetting behaviour was observed.

EXAMPLE 2

[0027] A corrosion test according to BS6920 was performed with ringsused in seal ring applications. The test comprised essentially thefollowing steps:

[0028] 1. Cleaning of the container with HNO₃ (10 vol. %) and deionisedwater.

[0029] 2. Cleaning of the sample with tap water (30 min) and rinse threetimes with deionised water.

[0030] 3. Immersion of the sample at room temperature during one day in500 ml of deionised water.

[0031] The rings are placed on PTFE supports (previously washed as inpoint 1) in order to maintain the rings vertically.

[0032] The test is done at room temperature and at 85° C.

[0033] 4. Transfer of all but 50 ml of the extract into a sample bottle(cleaned as in point 1).

[0034] Add 5 ml of HNO₃ (70 wt. %) to the remaining 50 ml in order toremove any metals adsorbed onto the surface of the container.

[0035] Add to the rest of the extract.

[0036] 5. Chemical determination of Co, Ni, Cr, Mo and Fe usingICP-spectrometry.

[0037] 6. Reimmersion of the sample at room temperature in new deionisedwater six times: five times for one day and once for three daysfollowing points 1, 2, 4 and 5.

[0038] 7. Blank test: following the point 1 to 5 without any sample.

[0039] Test material were rings with two dimensions:

[0040] OD=39 mm, ID=31 mm, height=3 mm (1540 mm²)

[0041] OD=40 mm, ID=30 mm, height=5 mm (2200 mm²)

[0042] The surface condition was as sintered.

[0043] Materials Used in the Corrosion Test:

[0044] Stainless steel AISI 316 (Fe: Cr18/Ni10/Mo3).

[0045] Plates of steel with about 9000 mm² total surface were usedinstead of rings in the leaching test with water.

[0046] Grade C6N with 0.55 wt. % Cr

[0047] Rings with the total area of about 15000 mm² were used during theleaching procedure.

[0048] This grade is a common used CC-grade in seal rings for pumps insalt and fresh water.

[0049] Grade C9M (9 wt. % of a Ni—Mo—Cr Binder) According to Prior Art(Example 1)

[0050] Rings with the total area of about 15000 mm² were used during theleaching procedure.

[0051] This grade is used in pumps for corrosive media especiallyseawater.

[0052] Rings According to the Invention (Example 1)

[0053] Rings with the total area of about 15000 mm² were used during theleaching procedure.

[0054] Results: Leaching No Analysis, μg/l 1 7 Stainless steel AISI 316Temp. 26° C. Co 220 <20 Ni 20 <20 Fe 150 <20 Cr <20 <20 Mo <20 <20 Temp.85° C. Co 60 <20 Ni 2320 <20 Fe 460 <20 Cr <20 <20 Mo <20 <20 Grade C6N+0.55 wt. % Cr Temp. 85° C. Co 480 <25 Ni 6000 210 Grade C9M (Prior art,Example 1) Temp. 85° C. Co 170 40 Ni 2920 570 Cr <20 <20 Mo <20 <20 Fe370 <20 According to the invention (Example 1) Temp. 24° C. Co 20 <20 Ni40 <20 Temp. 85° C. Co 180 <20 Ni 360 <20

[0055] These results show very good corrosion resistance for thecemented carbide according to the invention:

[0056] At room temperature, the Co and Ni concentrations are lower tothe limit of 50 μg/l or lower to the detection limit of 20 μg/l afterthe first and last leaching respectively.

[0057] At higher temperature, the Co and Ni concentrations are quitehigh after the first leaching, but below the detection limit after thelast leaching.

[0058] The cemented carbide can be approved under the BS6920 standard.

EXAMPLE 3

[0059] The resistance to abrasive wear was investigated with a cratergrinding test as follows.

[0060] The test equipment consists of a stainless steel wheel with adiameter and width of 20 and 2 mm, respectively. The wheel has a roundedrim surface with the same radius as the wheel, thus shaped as if cut outfrom the centre of a sphere. The specimens were glued to a horizontaltable, which was also rotated during the test. Abrasive slurries wereapplied between wheel and specimen surface. The combined rotary motionresulted in a wear scar the shape of a spherical cap, some 1 mm indiameter, on the specimen surface.

[0061] The abrasive wear particles are monocrystalline diamond of a gritsize of 2.5 μm. These particles are mixed with a commercial standardliquid (KEMET TYPE 0), to a concentration of 25 g/l. The normal load was0.2 N and the total sliding distance was 50 meter (800 revolutions).After every 12.5 m the test was stopped, the crater diameter measuredwith optical microscopy and new slurry deposited on the specimen. Thevolume loss was measured with an optical surface profilometer.

[0062] The cemented carbide rings from example 1 were tested accordingto mentioned test method:

[0063] Results from the small scale abrasion wear test: SpecimenRelative wear Grade SANDVIK C10C 1.00 Grade C9M (prior art, Example 1)0.87 According to the invention 0.93 Stainless steel AISI 316 8.3 

[0064] The relative wear is less for the cemented carbide according tothe invention. Thus, the new grade has both better corrosion resistanceand better wear resistance than the grade C9M.

[0065] While the present invention has been described by reference tothe above-mentioned embodiments, certain modifications and variationswill be evident to those of ordinary skill in the art. Therefore, thepresent invention is limited only by the scope and spirit of theappended claims.

We claim:
 1. A corrosion resistant carbide seal ring comprising a hardphase and a binder phase, the ring having a high resistance to leachingsuch that less than 50 μg/l of each of Fe, Ni and Cr leaches intodeionised water at 85° C. when subjected to the procedure set forth inBritish Standard BS6920, Section 2.6,
 1996. 2. The cemented carbide sealring according to claim 1, wherein the ring has content of binder phaseof 5-15 wt. %, with the remainder WC with an average grain size of 1 μmto 5 μm, and the binder phase has a composition comprising 35-45 wt. %Fe, 15-50 wt. % Co and remainder Ni.
 3. The cemented carbide seal ringaccording to claim 2, wherein the content of binder phase is 8-11 wt. %.4. The cemented carbide seal ring according to claim 2, wherein thecontent of binder phase is about 9 wt. %.
 5. The cemented carbide sealring according to claim w, wherein the binder phase has a Fe/Ni ratio of1-1.3.
 6. The cemented carbide seal ring according to claim 5, whereinthe binder phase contains Cr.
 7. The cemented carbide seal ringaccording to claim 6, wherein the binder phase contains Cr in an amountof 0.05<wt. % Cr/(100-wt. % WC)<0.15.
 8. The cemented carbide seal ringaccording to claim 7, wherein the Cr amount is 0.055<wt.% Cr/(100-wt. %WC)<0.11.
 9. The cemented carbide seal ring according to claim 7,wherein the Cr amount is 0.065<wt. % Cr/(100-wt. % WC)<0.085.
 10. Thecemented carbide seal ring according to claim 5, wherein the binderphase contains Mo.
 11. The cemented carbide seal ring according to claim6, wherein the binder phase contains Mo in an amount of 0.1-3 wt. %. 12.The cemented carbide seal ring according to claim 11, wherein the binderphase contains Mo in an amount of <0.5 wt. %.
 13. The cemented carbideseal ring according to claim 1, where the ring comprises a total carboncontent in the interval of 6.13-(0.05±0.007)×binder phase (Co+Ni+Fe)content (wt. %).
 14. The cemented carbide seal ring according to claim1, wherein the ring has a graphite porosity <CO2 in the interior of thering.
 15. The cemented carbide seal ring according to claim 14, whereinthe ring has a surface zone >200 μm thick which is free of graphiteporosity.